Cryogenic Ion Spectroscopy of Peptides and Glycans

Understanding the structure of biomolecules, which are directly related to physiological processes that take place in the human body, has always generated a large interest in the scientific community. In this thesis we focus our attention on two of these classes of biomolecules: peptides and glycans. In the first part of this work we investigate how the structure of helical peptides in the gas-phase is modified when one increases the number of amino acids in the sequence. Moreover, we analyze the role played by a mobile charge in the formation of the helical motif in the gas-phase. To achieve these goals, we make use of a home-built tandem mass spectrometer, and a pump-probe laser spectroscopic scheme. The combination of infrared and ultraviolet light together with cryogenic temperatures allows one to collect high-resolution conformer-specific spectra of gas-phase peptides. By comparing the experimental results obtained with density functional theory calculations, we show that the synergy between theory and experiment is key to provide accurate structural characterization of the investigated peptides. The mobile charge, in fact, induces unconventional backbone conformations, which cannot be predicted a priori by performing experiments alone. In the second part of this thesis we present a novel technique to identify and characterize glycans in the gas-phase that exploits a database approach. Due to their structural heterogeneity, glycans pose a problem for the currently available mass- and mobility-spectrometry techniques. In the work herein we show that we can easily identify glycan structural isomers, by adding a spectroscopic dimension to mass and mobility measurements. Cryogenic vibrational messenger spectroscopy, in fact, allows us to unambiguously identify disaccharides and pentasaccharides isomers due to the high-resolution provided by this method. Moreover, we can perform our experiments in a broad range of temperatures, going from liquid helium to liquid nitrogen. This shows the potential of our technique in becoming a more accessible analytical tool for glycan identification.